The overall goal of Core B, Scientific Services, is to provide shared scientific services for the individual scientific projects. This core is essential to the overall success of the Program Project. It makes five important contributions: First, by combining resources, it provides an economy of scale. Second, by providing well maintained facilities, it saves time and makes each program member more efficient. Third, by supporting trained technical support staff, it provides technical expertise, which is of benefit to all program members, and especially when new members arrive. Fourth, by providing quality control of shared reagents, the success rate and reproducibility of experiments is higher and the results of members in different projects can more easily be directly compared. And, fifth, shared facilities facilitate the exchange of experimental ideas, methodology, and results, and limits the recurrence of experimental problems. Every project in this Program Project benefits from the Scientific Services Core. It provides: (1) Cell culture and virus production facilities. (2) Microscopy services and expertise. (3) Bioinformatics services and expertise. (4) Instrumentation support.